Basic Organic Chemistry: Free Radical, Carbocation

Free radical

It is an atom within paired (odd electrons in valence shell) electrons. Free radicals are not stable which makes them highly reactive species. Free radicals are formed when one of the weak bonds is broken and an odd number of electrons remains in the valence shell of the bonded atoms. During a homolytic cleavage, one of the electrons from the shared pair in a covalent bond goes with each of the atoms which are bonded. Instead of an electron pair, there is a movement of a single electron. Half-headed curved arrow is used to show the movement of a single electron.

What are carbocations?

A carbocation is that molecule in which the carbon atom acquires a positive charge and also bears three bonds such that it has a sextet of electrons.

Carbocations are classified into three categories:

Primary carbocation: The positively charged carbon atom is attached to only one alkyl group. This is also called 1o carbocation.

Secondary carbocation: The positively charged carbon atom is attached to two alkyl groups. This is also called 2o carbocation.

Tertiary carbocation: The positively charged carbon atom is attached to three alkyl groups. This is also called 3o carbocation.

What are carbanions?

A carbanion is that molecule in which the carbon atom bears a negative charge. Carbanions being nucleophiles, their stability depends upon various factors:

Inductive effect: If an electronegative atom is near to the charge then it will stabilize the molecule.

Hybridization of the charge bearing atom.

The extent of conjugation.

Electrophile: An electrophile is that molecule or ion which has the ability to accept electrons and form a new covalent bond. Any molecule which is electron deficient can be an electrophile. It acts like a Lewis acid

Nucleophile: A Nucleophile is that molecule or ion which has the ability to donate electrons and also form a new covalent bond. Any molecule or ion that has an extra pair of electrons to share can be stated as a nucleophile. It also acts like a Lewis base.